Wells for recovering oil, gas and the like are typically drilled by a drilling rig which includes a hollow drill string with a bit at its lower end. As the drill string is rotated, drilling fluids are pumped down through a channel in the drill string. The drilling fluids pass through the bit and return to the surface on the outside of the drill string. The fluids carry cuttings from the drilling operation to the surface. The drilling fluids are recovered at the surface and then recycled. Water may be used as drilling fluid in shallow drilling. In deeper wells the drilling fluids are denser drilling muds of various compositions as is known to those skilled at drilling wells.
Various apparatus and methods are known for removing cuttings and other undesired solids from drilling fluids so that the drilling fluids may be reused. A widely used method for removing solids from drilling fluid is to pass the recovered drilling fluid through a centrifuge. The centrifuge separates the undesirable solids from the drilling fluid. The drilling fluid output from the centrifuge may then be reused. Because of the volume of drilling fluid used in a typical well drilling operation, it is necessary to either have a very large centrifuge system or to provide multiple centrifuges. The costs of having a centrifuge system on site and operating the centrifuge system are significant. There is a need for a solids separation system capable of removing solids from drilling fluids which can be provided and operated at reduced cost relative to prior art systems.